Cobalt in north-east Pacific waters

Abstract

Significant understanding has been gained recently about the biogeochemical cycling of trace metals in the ocean. This knowledge has mostly resulted from the accurate measurement of dissolved species in oceanic water columns. We report here that cobalt's vertical distribution is similar to that exhibited^1–3 by Mn; that is, its surface enrichment/deep depletion (Fig. 1). However, amounts of Co (1–7 ng 1⁻¹) are ∼10–20 times less than those for Mn (Table 1), as might be expected from crustal abundance estimates⁴ for these elements (Mn=950; Co = 25 µg per g). The similarity between Mn and Co profiles implies the same biogeochemical pathways. The Co excess in nearshore surface waters probably results from continental weathering input processes, as suggested by the remarkable Co–salinity mirror-image relationship shown in Fig. 1, and the Co–salinity scatter diagram in Fig. 2a. The steady decrease in Co concentrations also indicates that Co is usually scavenged rather than regenerated at depth, as is the case with Mn (Fig. 1; Table 1).